Cover crop and rotation intensity effects on soil health and yield in corn-soybean cropping systems

Abstract

In the Midwest, corn-soybean [Glycine max (L). Merrill] is the dominant biennial cropping system, which covers approximately 75% of the arable land surface (Hatfield et al., 2007; Plourde et al., 2013). The growing demand for corn (Zea mays L.) and its financial competitiveness as a cash crop over the past two decades has led to an increased use of more corn-intense cropping systems. This increase in corn intensity within corn soybean rotations in the Midwest has caused concern for maintaining soil health and cash crop yields for the long-term. The implementation of cover crops and crop rotation are widely promoted management strategies that have been shown to enhance soil health in agricultural systems, and may lead to increases in cash crop yields. The objectives of Chapter II of this dissertation were to examine the influence of cover crops, crop rotation, year, and their combination on several soil health indicators and cash crop yield. The soil health indicators of bulk density, water stable aggregates, soil moisture, total organic carbon, active carbon, potentially mineralizable nitrogen (PMN), and soil microbial community composition via a phospholipid fatty acid (PLFA) analysis were measured in 2017 and 2018 in Columbia, MO under no-till conditions. Grain yields of corn and soybean were recorded from 2016-2019. Crop rotation treatments significantly improved water stable aggregates and corn yield. Cover crop treatments led to significant improvements in several soil health indicators (water stable aggregates, soil moisture, PMN, AMF, gram negative bacteria, and the gram positive / gram negative ratio) while maintaining yield in soybean and decreasing yield in corn. The objectives of chapter III of this dissertation were to evaluate the long-term effects of increased corn frequency within a corn-soybean rotation on several soil health quality indicators and evaluate the long-term corn and soybean yield responses to ten different corn-soybean rotations. In order to better represent the long-term impacts of increased corn rotation intensity within rotations on soil health, corn rotation frequency (CRF) ratings were assigned to each rotation treatment based on the percentage of corn within each rotation. Utilizing these ratings when evaluating the soil data allows for effects of increased corn within rotations to be more easily identified. Soil measurements were taken in 2014 and included several indicators of soil physical, chemical, and biological health to provide a snapshot of conditions as a result of nine years of the ten rotation treatments being in place. Yield data was collected from 2007 – 2019 to evaluate the long-term effects of various corn intensities within corn-soybean rotations. Overall, corn yields were significantly improved in the first year after soybean, and with fewer consecutive years of corn in the rotation cycles. Soybean yields were most significantly improved after following two years of corn, and when avoiding consecutive years of soybean. Although the two-year corn-soybean rotation yields were statistically similar to soybean following two years of corn in 9 of 11 years in this study. For soil measurements, significant improvements from increased corn rotation intensity were seen in bulk density, total nitrogen, PMN, TOC, active carbon, SOM, [beta]-glucosidase, overall microbial biomass and diversity, AMF, gram negative bacteria, gram positive bacteria, and actinobacteria. These results provide valuable information to producers aiming to improve soil physical, chemical, and biological function while also maintaining the highest yield potential in corn-soybean rotations.